Minimum-oil circuit breaker including movable contact rod with elastically deformable braking member for applying braking force thereto proportional to gas pressure generated in arc-quenching chamber

ABSTRACT

A circuit breaker of the minimum-oil type includes a chamber for quenching the arc drawn between a movable contact rod and a stationary contact as the two separate. To counteract and damp the acceleration effect produced on the movable contact rod within the quenching chamber as a result of gas pressure built up within the chamber due to arc action, a softly elastic annular damping member closely surrounds the movable contact rod and is deformed in a radially inward direction by the gas pressure to press against the movable contact rod and hence provide a braking action for the rod. The radially inward deformation of the elastic damping member is proportional to the gas pressure produced in the quenching chamber and hence provides a braking effect on the movable contact rod which desirably increases with an increase in gas pressure.

United States Patent Latal et al.

MINIMUM-OIL CIRCUIT BREAKER INCLUDING MOVABLE CONTACT ROD WITH ELASTICALLY DEFORMABLE BRAKING MEMBER FOR APPLYING BRAKING FORCE THERETO PROPORTIONAL TO GAS PRESSURE GENERATED IN ARC-QUENCI-IING CHAMBER Inventors: Werner Latal, Wettingen; Willi Schneebeli, Zurich, both of Switzerland Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland Filed: Aug. 19, 1971 Appl. No.: 172,970

Assignec:

Foreign Application Priority Data Sept. 10, 1970 Switzerland 13472/70 References Cited FOREIGN PATENTS OR APPLICATIONS 2/1929 Germany 200/151 R 1,298,176 6/1969 Cverrnany 200/150 B Primary Examiner-Robert S. Macon Att0rneyPierce, Scheffler & Parker [57] ABSTRACT A circuit breaker of the minimum-oil type includes a chamber for quenching the arc drawn between a movable contact rod and a stationary contact as the two separate. To counteract and damp the acceleration effect produced on the movable contact rod within the quenching chamber as a result of gas pressure built up within the chamber due to arc action, a softly elastic annular clamping member closely surrounds the movable contact rod and is deformed in a radially inward direction by the gas pressure to press against the movable contact rod and hence provide a braking action for the rod. The radially inward deformation of the elastic clamping member is proportional to the gas pressure produced in the quenching chamber and hence provides a braking effect on the movable contact rod which desirably increases with an increase in gas pressure.

3 Claims, 2 Drawing Figures MINIMUM-OIL CIRCUIT BREAKER INCLUDING MOVABLE CONTACT ROD WITH ELASTICALLY DEFORMABLE BRAKING MEMBER FOR APPLYING BRAKING FORCE THERETO PROPORTIONAL TO GAS PRESSURE GENERATED IN ARC-QUENCI-IING CHAMBER This invention relates to an improved construction for a minimum-oil circuit-breaker having one or more quenching chambers and a source of power to actuate the contact rod.

In minimum-oil circuit-breakers, the opening movement of the contact rod gives rise to an are between the fixed contact and the moving contact rod. Because of this arc an elevated pressure occurs in the quenching chamber which also acts on the cross-section area of the contact rod. Particularly in medium voltage circuitbreakers, which require comparatively small forces to operate them, this pressure can cause high acceleration of the contact rod movement. As a result of this, the arc can be greatly elongated and be drawn out of the quenching chamber, and safe quenching of the arc can no longer be assured.

A technique of avoiding these disadvantages is already known whereby damping elements are fitted in the breaker operating mechanism. This mechanism may be spring-powered or operated by hydraulic or pneumatic means. The purpose of the damping elements is that the velocity of the contact rod on opening.

should not significantly exceed the optimum value.

A disadvantage of this arrangement, however, is the fact that the operating mechanism must be made considerably stronger because with every switching operation, including those where only little or no pressure occurs in the quenching chamber, the friction losses of the damping elements must be compensated by the operating mechanism.

The purpose of the invention is to create an arrangement which does not exhibit the disadvantages and shortcomings of the known solutions.

In accordance with the invention this purpose is achieved by locating in the breaker housing a damping element which is responsive to pressure and acts as a brake on the movable contact rod.

The advantage of the invention is in particular that the damping element acts as a brake only in those cases where the contact rod movement is accelerated by increased pressure in the quenching chamber, and that in such cases the braking effect is proportional to the pressure in the quenching chamber, and hence to the force, resulting from this pressure, which causes the contact rod to accelerate.

It is of particular advantage to locate the damping el ement at the opening in the quenching chamber cover through which the contact rod passes. With this arrangement, on the one hand, the excess pressure is converted to a retarding force direct at the place of origin, while on the other hand, the contact rod can move unhindered in the event of switching operations which do not cause elevated pressure in the quenching chamber.

According to a preferred form of the invention the damping element is composed of an elastic material and is in the form of an annulus which closely surrounds the movable contact rod. When a relatively soft elastic material is used, for example rubber, cork or various synthetic substances, the pressure occurring in the quenching chamber causes the annular damping element to deform press more, or less, firmly round the contact rod in accordance with the magnitude of the pressure produced in the quenching chamber, and so proportionately retard the contact rod movement.

A particular advantage of this arrangement is that, owing to the absence of damping devices in the operating mechanism which are active during every switching operation, the operating mechanism requires much less power and can therefore be made correspondingly lighter. The advantages of the arrangement according to the invention are especially evident in the case of threepole circuit-breakers where, for example, elevated pressure occurs in the quenching chamber of only one pole, because braking takes place only in that pole where it is actually necessary because of the higher pressure in the quenching chamber. This arrangement makes possible a significant lowering of cost, a reduction in design expenditure and hence simplification of the circuit-breaker as a whole.

The foregoing as well as other objects and advantages inherent in the invention will become more apparent from the following detailed description of a preferred embodiment thereof and the accompanying drawings wherein: I

FIG. 1 is an axial longitudinal section through a circuit breaker of the minimum-oil type in which the'improved gas pressure responsive braking structure for the movable contact rod according to the invention has been incorporated; and

FIG. 2 is a detail sectional view drawn to a larger scale illustrating the contact rod damping element itself.

With reference now to the drawings in which corresponding elements in both views have been designated by the same reference numerals, FIG. 1 illustrates the housing 1 for the circuit breaker contacts which is made from a suitable insulation material. Established within housing 1 is a quenching chamber 2 closed at the top by a cover 3 in which an opening 4 is provided that serves as an outlet for the gases formed by the arc produced upon disengagement of the contacts and also for the quenching fluid. Situated below the quenching chamber 2 are a pair of spaced stationary contact members 5 supported upon a projection 5a of a lower contact body 5b which terminates in one end connection terminal 8 for the circuit breaker.

A movable contact rod 6 is located centrally within the housing and is arranged to be displaced longitudinally by a suitable actuating mechanism, in itself known, and which has accordingly not been illustrated, into and out of engagement with the stationary contact members 5. The contact rod 6 passes through an upper contact body 9 the interior of which forms a gassettling chamber and which also contains a certain quantity of oil 10. A vent hole 11 to atmosphere is provided at the upper end of settling chamber 9a.

Surrounding contact rod 6 and engaged with the surface thereof are contact members 7 which serve to electrically connect contact rod 6 through the upper contact body 9 to the other end terminal 8 of the circuit breaker.

A spacer sleeve 12 of insulating material is located on the inside wall of the breaker housing 1 between quenching chamber 2 and its cover 3, and a similar spacer sleeve is located between cover 3 and the contact body 9 in which the settling chamber 90 is formed.

The annular and relatively softly elastic damping member 13 made from rubber, or cork or other material having a similar elastic characteristic which closely surrounds contact rod 6 and provides a variable braking force for the latter in accordance with the gas pressure developed within the quenching chamber is positioned in cover 3. The damping member 13 which has a conical configuration and is seated in a complementarily configured recess 3a in cover 3 is shown more clearly at larger scale in FIG. 2 in association with contact rod 6. The left half of FIG. 2 depicts the response of the elastic damping member 13 under dynamic conditions, i.e. the deformation thereof in a radially inward direction by the gas pressure (indicated by the arrows) to press against the contact rod 6. The right half of FIG. 2 shows the elastic damping member 13 under static conditions, i.e. no gas pressure from which it will be seen that the surface of contact rod 6 does not touch the wall of the central opening 13a in the damping member through which the rod passes.

Theoperating principle of the damping arrangement in accordance with the invention will now be described. When, during the opening process, contact rod 6 moves upwards, there occurs between contact rod 6 and fixed contact 5 an are which extends into quenching chamber 2. This are gives rise to an elevated pressure in the quenching chamber which during the upward movement of contact rod 6 acts on its crosssectional area and can greatly accelerate the movement of contact rod 6. The pressure created in quenching chamber 2 also acts on damping element 13 which, because it is of elastic material, is correspondingly compressed and deformed so that, as is shown in the lefthand half of FIG. 2, damping element 13 is pressed against the contact rod 6 and thus retards its upward movement. At the same time, the quenching fluid, together with the gases, is forced upwards through opening 4 and enters gas-settling chamber 9.

As soon as the switching operation is completed, and thus the are is extinguished, the pressure created in the breaker by the switching operation returns to normal and elastic damping element 13 again releases contact rod 6, as is shown in the right-hand half of FIG. 2.

In conclusion, it is to be understood that the invention is not restricted to the specific embodiment represented in the drawings. For example, damping element 13 could be located at some other position in circuitbreaker housing 1 and it could be of some other geometrical form, or of other elastic materials which deform to exert a braking effect on contact rod 6.

We claim:

1. In a circuit breaker of the minimum-oil type, the combination comprising a housing including a quenching chamber therein, a movable contact rod operable within said quenching chamber to engage and be disengaged from a stationary contact, and an annular elastic damping member closely surrounding said movable contact rod and which is deformable in a radially inward direction in response to a rise in gas pressure generated within said quenching chamber upon disengagement of said contact rod from said stationary contact to engage and apply a braking force to said contact rod which varies in accordance with the magnitude of the gas pressure.

2. A circuit breaker as defined in claim I wherein said quenching chamber includes a cover plate and wherein said damping member is supported by said cover plate at the opening therein through which said contact rod passes.

3. A circuit breaker as defined in claim I wherein said annulus of elastic material has a conical configuration and is seated in a complementarily configured recess in said cover plate. 

1. In a circuit breaker of the minimum-oil type, the combination comprising a housing including a quenching chamber therein, a movable contact rod operable within said quenching chamber to engage and be dis-engaged from a stationary contact, and an annular elastic damping member closely surrounding said movable contact rod and which is deformable in a radially inward direction in response to a rise in gas pressure generated within said quenching chamber upon disengagement of said contact rod from said stationary contact to engage and apply a braking force to said contact rod which varies in accordance with the magnitude of the gas pressure.
 2. A circuit breaker as defined in claim 1 wherein said quenching chamber includes a cover plate and wherein said damping member is supported by said cover plate at the opening therein through which said contact rod passes.
 3. A circuit breaker as defined in claim 1 wherein said annulus of elastic material has a conical configuration and is seated in a complementarily configured recess in said cover plate. 